The present invention relates to radio frequency (RF) or microwave switching, and more particularly to a high isolation RF switch to provide for dual launch of RF signals into a slabline transmission line structure.
Previously an RF slabline transmission line structure had a single input port and a single output port with a slabline transmission line between them for coupling an RF signal from the input port to the output port. In order to provide for dual launch of RF signals into the slabline transmission line structure, a pair of input ports and an appropriate switch are required to couple a selected one of the RF signals to the output port via the slabline transmission line. A separate component, usually a coaxial switch external to the slabline transmission line structure, may be used as the appropriate switch. Using an external component adds size, weight and cost as well as insertion loss due to the necessary connectors and cabling. Such coaxial switches generally are a make or break architecture where one input port is left as an open circuit when the other input port is coupled to the output port via the slabline transmission line. Whether the coaxial switch is external or integrated with the slabline transmission line structure, the open circuit of the non-selected input port acts as a radiator with the other input port acting as an antenna to receive the RF signal from the non-selected input port, i.e., some of the RF signal from the non-selected input port is coupled to the RF signal from the selected input port. FIG. 1 illustrates a poor isolation characteristic S21 between the input ports in this dual launch make/break switching configuration, being as small as 3 dB at 14 GHz. Ideally there should be a large amount of isolation between the input ports.
What is desired is a high isolation RF switch for launching a selected one of two distinct RF signals into a slabline transmission line structure.